Method of drawing metal



Patented Mar. 4, 1952 METHOD OF DRAWING METAL John A. Henricks, Cleveland, Ohio N Drawing. Application October 31, 1950, Serial No. 193,290

13 Claims. (Cl. 148-615) This application is a continuation-in-part of my copending application Serial No. 665,905 filed April 29, 1946. The invention relates to the lubrication of sliding metal surfaces. In particular, it relates to the treatment and lubrication of surfaces under conditions of extremepressure and surface temperature as encountered in the drawing and deforming of metals such as steel.

Ordinary lubricating oils fail to give satisfactory performance characteristics in the drawing and deforming of harder metals such as steel with the result that tearing of the metal or galling of the dies frequently occurs. Even extreme pressure lubricating oils are unsatisfactory for this purpose and are not recommended. The accepted theory is that the failure of such lubricants is due to a squeezing-out of the lubricants from between the work and die because of the extreme pressure used. Accordingly, to counteract this extreme pressure and to prevent the squeezingout of lubricants, it has been the general practice to utilize as drawing compositions lubricants containing infusible pigments such as clay, lime, mica, calcium or magnesium carbonates, titanium dioxide and graphite. The function of such pigments is to separate the die and the workpiece at points of extreme deformation and intimate contact when the pressure or temperature is too great to be withstood by the organic constituents of the lubricating material. While such compositions do function better than the prior non-pigmented materials, an examination of the work drawn with the aid of such drawing compositions discloses minute particles of pigments embedded therein and a surface with an undesirable dull finish.

This readily explains the galling of dies and the welding and seizure of moving parts. From this it can be seen that the failure of a drawing lubricant may well be caused by high temperature destruction or carbonization of the lubricant with the resultant gallingand seizure instead of pressure squeezing-out the material from the working surfaces as previously believed.

From this it follows that for the most satisfactory drawing and working of metal, effective lubrication throughout the entire temperature range below the melting point of the work or die is desirable. Furthermore, neither the drawing lubricant nor the surface of the metal should contain any solids capable of scratching the sur face of the metal.

An object of the present invention is to provide a method of drawing metal wherein the metal is lubricated throughout all temperatures below its welding pointso that relatively smooth working of the metal isfacilitated and there is no galling, seizing, or scratching of the metal or die and a smooth shiny surface is produced on the metal.

A further object of the present invention is to utilize a drawing lubricant containing ingredients which function to provide lubricating and cooling properties throughout the different temperature ranges by their ability to melt and flow under frictional heat andto provide a method of drawing metal whereby the workpiece and die are subjected to a stepwise lubricating action of materials which function to give optimum lubricating properties throughout the different temperatures.

Another object is to provide a process of drawing and forming metal wherein a smooth finish is obtained on the drawn article and wherein the residual fusible integral film on the metal forms a desirable base for paint or enamel coatings so that the drawn article may be painted without the necessity of first cleaning the surfaces thereof or so that the fusible lubricant coating acts as a prime coating to provide superior adhesion of subsequent paint or lacquer films.

In accordance with the present invention, I form an integral meltable film directly on the surface of the workpiece, and coat this with a suitable organic binder through which is disposed pigments of distributed melting points. The integral coating formed on the surface of the work and the pigments in the binder are of materials having a hardness less than 5 on Mohs scale and melting at temperatures below that of the die or the workpiece, whichever melts at the lower temperature. Likewise, the organic binder melts or decomposes at temperatures below that of the fusion of the fusible pigments. The melting points of the integral coating, organic binder, and incorporated solids are determined and arranged or graduated so that they melt in successive tem perature ranges and there is a plastic lubricant between the die and workpiece at all temperatures and stepwise lubrication is achieved.

The process thus embraces three basic, co-acting factors. In the first place, there is an integral coating formed directly upon the work. In the second place, an organic binder is disposed over the work. And thirdly, meltable pigments are dispersed in the organic binder to further lubricate and facilitate drawing and deformation of the work. In this way, the Work is lubricated and protected throughout the drawing or forming process and superior draws are made possible.

Various materials and processes can be used to form the coating directly on the work surface and several resultant coatings can be employed. The qualifications of the integral coating or fixed film are that it must have a hardness less than 5 on Mohs scale and that it will be plastic at temperatures below that at which the work or die welds.

INTEGRAL COATINGS The formation or integral coatings on ferrous metals is brought aboutby'an unusual elec trochernical phenomenon. The usual corrosion of metals involves a well understood galvanic action between local cells or couples on the metal surface in which specific areas of the metal become anodic because of differences in chemical composition, intergrariular strain, or local oxygen concentration, and iron goes into solution and the equivalent hydrogen ions are discharged at the less reactive cathodic areas.

The ror'inaucn of tarnish films and integral coatings onpolyvalent metals involves the Wag ner electrolytic theory. "C. Wagner studied this phenomenon and proposed an explanation reported in the transactions of the Faraday Society 34, 851 (1938) and elsewhere. Unlike the local galvanic cells existing in the usual corrosion of metals, the corrosion product or tarnish film is built up by "a mechanism wherein the metal-t0- filin interface becomes the anode and supplies cations andelectrons for outward diffusion, and the attacking 'filni substance-to-environment interface beceines the cathode and supplies anions for inward diffusion. Tli'egfOWihgfilmthus acts as both the internal and external circuits of a closed cell. The internal "cellbircuit is made possible by the insoluble iron compounds acting as a semi-conductor, while the conducting electrolyte in. the film pores and capillaries furnishes an external eircuit. The Wagner tarnish 'm'echafhisin requires {an attack by a diacidic metallic precpitaung reagent in order-to form thesemiconducting metallic component of the internal circuit. Thus, when the polyvalent metal is ferrous, the integral coating will always contain iron salts. The cathodic film-to-solution interface contains the discharging hydrogen, 'so that any depolarizer in the solution effectively accelerates the coating action.

The principal object 'of this invention is to utilize the Wagner mechanism to convert an otherwise refractory metal surface into an inte- 'gral film of "suitable compounds that will absorb and t'en'aciously hold a thermoplastic lubricant 'fihn containin'g other fusible pigments.

When such a fillh is to be formedin aqueous 'n'iedia, the diacidic precipitating reagent can be selected from the difiuorides, the various dihyerogeh phosphates, the dicarboxylic organic" acids,and the dibasic inorganic sulfur containing acids ranging from hydrogen sulfide through sulfcxylic to the various polythionic acids.

Tarnish films of mixed oxides are also formed in the gaseous phase by the Wagner mechanism IRON SULFIDE CoATiNos The most versatile lubricant base integral coating is that consisting principally of iron sulfide since it can be applied in either aqueous, gaseous, or molten salt-media.

v Whenferrous metals are to be coated with a fusible integral iron sulfide film in aqueous media, I utilize an acidic solution containing colloidal sulfur, sulfur dioxide, and a mixture of polythionic acids. Such a solution can be prepared by the acid decomposition of unstable inorganic sulfur compounds by any of the following methods:

1. Sodium thio's'ulfate or Sodium pommmmtes decomposed by preferred dibasic acids which are also coating agents.

2. Decompositionof equimolar HzS and S02 in aqueous acid solution to give Wackenroders solution.

3. Hydrolysis of sulfur mono-chloride emulsi fied in a dibasic acid solution to form polythionic acids.

4. Interaction of 'wettable sulfur and sulfur an." oxide in a solution containing a dibasic coating acid. J

Integral ferrous sulfide films can also be formed on still or iron hydroxide coated ferrous metal by converting the hydrated iron oxide "film to iron sulfide by dipping in a 'hot aqueous alkaline polysulfide solution.

When ferrous metals are filmed with a layer of sodium thiosulfate or an equivalent decomposable sulfur salt, the metal can be coated with-an integral coating of "iron sulfide by heating the filmed metal above the initial melting point of the hydrated salts which melt in their water of crystallization. Likewise, a molten salt bath com taining active sulfur can be utilized. When rerrous metals are to be coated with a sulfideco'ating in gaseous media, a reducing atmosphere containing sulfur vapor is used and either the bare iron surface "i filmed with iron'sulfide or the hot mill scale-on the metal surface from previous operations can be converted to iron sulfide to act as a lubricant undercoat using a sulfur or phosphorus halide catalyst if required.

INTEGRAL PHOSPHATE AND OXALATE COATINGS Two types of phosphate coatings are utilized as lubricant bases in metal drawing and cold extrusion. The first type is a light coating of about 25 to mg. per sq. ft. formed by treating steel surfaces in a hot aerated or accelerated aqueous solution of 1 to 5 per cent sodium or ammonium dihydrogen phosphate. The second type is a heavy coating of about 206 to 1000 mg. per'sq. ft. of mixed zinc and iron phosphates formed by treatment of steel surfaces in'hot aqueous ja'ci'du} lated 1 to 5 per cent zinc dihydrogen phosphate accelerated by a strong oxidizing agent such as chlorate, persulfate, hydrogen peroxide, or a mixture of nitrate'and nitrite. The phosphate coatings from these baths are heavier because free acid is consumed by the iron surface acting as anode in the Wagner mechanism so that zinc phosphate precipitates upon the work alongwith the iron phosphate formed by the neutralization of the free acid essential to zinc phosphate solu-' bility. The amount of iron dissolved aslanode' in a zinc dihydrogen phosphate bath has been reported by Murphy and Streicher who showed (Proceedings Amer. Electroplaters $00., p. 288; 1948) that an average phosphate coating from a zinc phosphate bath had a coating thickness of 0.055 m. m. which represented an etched depth of 0.050 'm. m. and a dimensional increase of only 0.005 m. m. i

When a phosphate undercoat is desired as a component of my stepwise lubricant film, I can use any of the various proprietary coating baths in the patent literature such as those of Tanner and Lodeesen U. S. Patent No. 1,911,726, or Romig Patent No. 2,132,439; or I can use certain novel baths using Roussins salts or nitrosyl chloride as the accelerator; or a novel bath of immersion copper plate codeposited with iron phosphate which actsboth as a galvanic accelerator and a low frictional surface component.

Similarly, the proprietary oxalate coating baths such as that of Curtin and Kline U. S. Patent No. 1,895,568 or of Tanner U. S. Patent No. 1,911,537 can be used to obtain an integral oxalate coating as a component of a stepwise lubricant film. A novel method of obtaining an integral oxalate is to thermally decompose an aqueous layer of ferric oxalate, calcium chloride and oxalic' acid upon the work to form an insoluble film of mixed calcium and ferrous oxalates.

When an oxalate undercoating is used as a component of a stepwise lubricant, it is most desirable to convert the film to a more fusible form by dipping the coating in a hot alkaline aqueous solution of a sulfide, borate, or phos phate to convert iron oxalate to a fusible iron borate, sulfide, or phosphate and to a meltable sodium oxalate which in turn is thermally decome posed to fusible sodium formate and sodium carbonate under frictional heat.

The various methods of converting a refractory ferrous metal surface to a fusible iron compound which will imbibe and anchor a stepwise lubricant composition is illustrated in the following examples:

EXAMPLE I SULFIDE COATING ON STAINLESS STEEL FA sulfide coating bath for stainless steel was made up as follows: I

Wt. Oz.

I Molar Per Gal."

Iron chloride (FcCl -HzO) 0.3 5.0

Fluoboric acid (50% HBF 0. 3 6.0

Sodium thiosulfate (Na2S2Oa-5H20) 0.05 l

The sodium thiosulfate was added to the aquepickled 18-8 stainless steel tubes were immersed in the bath for six minutes, and removed to drain the points of the tubes to assure inside diameter coating, and the tubes again immersed in the solution for six more minutes to complete the coatingoperation. The lift of tubes were again.

cated with the drawing composition shown in Example XIII, after which they were dried and successfully drawn to a 38 per cent reduction at a speed of 50 feet per minute to produce a bright unscratched surface.

VAPOR PHASE SULFURIZING Vapor phase or gas-sulfurizing reactionv can also be used to coatthe metal with a sulfideifilm. The reaction is carried out by subjecting the work to sulfur or sulfur containing compounds in a heated reducing or non-oxidizing (inert) atmosphere. The sulfur can be applied as a coating before heating the work, or bled into the reducing atmosphere from a separate vapor generator. Hydrogen, hydrocarbon gases, carbon monoxide, ammonia or the oil vapors or other vapors come monly used for reducing atmospheres in the bright annealing of ferrous metals are satisfactory as reducing atmospheres during the reaction between sulfur and the ferrous metal. The attack of iron by sulfur begins at about 400 F. and increases rapidly up to about-950 F.

One advantage of my vapor phase sulfurization treatment in a-reducing atmosphere is that I may utilize metal from which the scale has not been removed as well as clean metal. Instead of removing the scale with an acid or surface 1 treatment, I am able to convert the scale directly into the desired ferrous sulfide. A trace of water or water vapor to initiate the reaction is usually necessary in order to obtain eflicient reduction of the iron oxide of the scale to ferrous sulfide. With high chromium and stainless steels, a catalyst such as phosphorus, halogen, a phosphorus or a sulfur halide or other suitable corrosive compound containing such elements is desirable to promote the reaction.

The atmosphere itself should be a reducing or a neutral, non-oxidizing atmosphere. An oxidizing atmosphere forms hard, undesirable ferric oxide and sulfide compounds such as iron pyrites or magnetic iron scale EXAMPLE II SnLruRIzrNc m at/moms ATMOSPHERE Hot rolled 188 stainless steel rod coated with mill scale is placed irijan annealing furnace at an atmosphere of per cent disassociated am monia and 25 per cent nitrogen and heated up to 1250" F. Free sulfur vapor is introduced from a generator containing boiling elemental sulfur and sulfur monochloride (liquid S2C12) is separately dripped into the furnace to furnish a sulfur halide catalyst to reduce the scale and assist its conversion to iron, chromium and nickel sulfides. The furnace temperature is kept between 1250" and 1800" F. for 10 to 25 minutes and then the work is removed. It is found to be coated with a relatively thick, fixed layer of mixed metal sulfides.

EXAMPLE III SULFURIZING m BURNER GAS ATMOSPHERE The work is placed in an atmosphere of exhaust burner gas containing nitrogen, CO2 and excess air and heated up to between 900 and 1300 F. Sulfur vapor" from a vaporizer is bled into the mixed stack gases where it combines essence '7 with the oxygen of the excess :air to "produce "a reducing and sulfurizing atmosphere to form a 'complex layer of iron sulfide :on the ferrous surface after a few minutes exposure.

.Sunroarzmo BY THERMAL moomtosmo'n-op A SULFUR COMPOUND I Another method of forming an integral ferrous sulfide coatingupon ferrous metal's is to cover the workwith an alkaline layerof .a sulfurizing agent and then heat the work in an annealing furnace, or a flash baker.

After steel has been hot rolled and initially shaped-the pieces have to'be annealed to restore the ductility for further coldwork. In the vast majority .of cases, the anneal is performed in "an uncontrolled furnace at atmospheric pressure so that thework becomes heavily scaledand must be .pickled before further cold work or drawing can be performed. When the work is covered with an alkaline film of asul-fu'rizing agent and heated, however, the heavy scaled layer on the hot rolled steel is converted to ferrous sulfide and the work made ready for cold drawing and shaping. In this way, I eliminate the pickling step and utilize the annealing step to deposit a layer of ferrous sulfide on the metal.

The alkaline, sulfurizing agent consists of a fusible. alkali metal salt and areducible sulfur compound that will convert the ferrous layer to iron sulfide and alkali ferrates when heated to a red heat and thus give an integral coating which can be ,cold worked without harming the working tools and dies. The magnetic iron oxide usually formed during hot rolling and annealing is highly abrasive to tools and dies. In addition to the fusible alkali salts and sulfurizing agents; fusible pigments can be incorporated or dispersed into the alkaline layer. A combination of ..pig'- ments with an alkali coating is preferred for ca'r- 1 e bon steel while an unpigmented film can be used for stainless steel.- A suitable alkaline type coating is given below. The mole fraction of eachchemical is given so that chemically equivalent compounds can be This is made up into a per cent to 33 per cent aqueous solution and applied to the work by dipping in the hot solution prior to annealing. Tenth molar sodium borate or sodium silicate can be used as a fusible alkali salt component in place of the 0.1 mole tri-sodium phosphate shown. Likewise, the chemical equivalent sodium sulfide, sodium sulfite, polysulfide, or polythionate can be substituted for sodium thiosulfate. The free sulfur in the above formula will be taken up in any case to form sulfides and polythionates. This film has additional complex chemical reactions when the work is heated. Iron sulfide and alkali ferrates are formed and whe phosphates are used as the fusible salt. it is believed that some thiophosphates are formed. When sodium silicate is used as the fusiblesalt, certain ultramarine type silicates are formed.

The work is dipped in the solution which is heated up to 180 200 F. and the hot solution allowed to dry on the work before being placed in an annealing'furnace or passed through a con-- tinuous open flame gas'ann'ealer. r

EXAMPLE V INTEGRAL IRON FLUORIDE CoA-T'I'N'c Another readily applied integral coating an iron fluoride layer, This is appliedby immersing thewo'rk in a solution o'fsodium'aoid fluoride with sodium phosphite or sodium 'sulfit'e as the aceelerator as follows? I V 7 1 Dissolve 8 'to'32 ounces of sodium bifluoride and V4 to /2 ounce of sodium phosphite (-NaH2PO2 H20) or sodium sulfite in each gallon or water. immerse the work in this solution maintained be tween'120" and F. for 5 to 15 minutes and then dry. This will form an adherent inte ral coating of iron fluoride, containing some ferrous phosphite or sulfite.

INTEGRAL Prio'sruers COATINGS A predominately iron phosphate "film can be formed on ferrous stock by dipping it in solution of a diacidic phosphate such as sodium dihydrogen phosphate, potassium dihyd'rog'en phosphate. ammonium dihydrogen phosphate, magnesium dihydrogen phosphate or calcium dihydrogen phosphate accelerated with an oxidizing or reducing agent.v :Su'itable oxidizing agents are sodium chlorate, sodium nitrite, sodium nitrate, hydrogen peroxide, potassium persul'fate, picric acid; qui none, and various other chlorates, bromates and ioda'tes Likewise, suitable reducing agents are sodium sulfite, sodium thiosulfate, and sodium phosphite.

EXAMPLE VI IRON PHOSPHATE Con-mo Parts (NHUI-IzPOs 75 cacl 11 H2O has .IIs s lu ==s c 14 This is made up 5 per cent by volume into an iron phosphating solution. This bath could be accelerated by bubbling in gaseous nitrosyl chloride or by adding aqueous nitrobetaine, or NOCl amine complexes or Roussins salts which are nitroso complexes of iron and sulfur. These are further described on page 678 of the Fritz EXAMPLE v11 COPPER IMMERSION PHOSPHATE- 7 Per cent Mono-sodium phosphate .l flashbacks 3 Copper sulfatelcslwph sl s .cc sless 0.1

This bath should be maintained at around 180" Theintegral coating of immersion copper mixed with copper and iron phosphates formed Zmc PHOSPHATE BATH Per cent Zn(H2PO4)2 3 NaClOs .6

, Maintain this bath at 160 to 180 F. and imrnerse the pickled stock for 5 to minutes to form an integral coating of mixed iron and zinc phosphates.

. Phosphate coatings are particularly valuable for drawing and cold working of metal because after the drawing or cold working has been completed, the phosphate coating forms a protective and anti-corrosion layer. It is also a very good base over which to applythe binders used in my stepwise lubricants. The phosphate baths, however, do not coat over stainless steel, so that oxalate, sulfide or fluoride baths must be used on these alloys.

INTEGRAL ORGANIC Acrn COATINGS Other integral coatings can be formed on the metal by treatment with selected organic acids. This process is fully explained in Patent No. 1,911,537 to Robert Tanner. Briefly, it consists of immersing or spraying the metal with a hot solution of aliphatic series acids with dicarboxyl groups or hydroxydicarboxyl groups or with aromatic series acids with one, carboxyl group or sulphonic acids. The reaction is preferably accelerated with an oxidizing agent such as man-- ganese dioxide or sodium sulfite and varies with each acid used. The best of the pure hot solutions are oxalic, malonic, tartaric, salicyclic, gallic', and diglycollic acids.

1 The coatings formed are mainly iron salts of the'acids used. Thus oxalic acid forms ferrousferric oxalate, tartaric acid ferrous-ferric tartarate and so forth. These organic iron salt films are thermoplastic or meltable by. secondary reactions largely based upon the splitting off of fusible organic acids under heat, but augmented by the thermal formation of fusible sodium formate and sodium carbonate. In addition, the strong reducing action of the thermally decomposed organic iron salts causes the formation of fusible ferrous oxide melting at 142.0" C. instead of the infusible ferric oxides. While such organic iron coatings are fluxed by binder-lubricants such as soap-borax mixtures and form additional low melting eutectics with any residual ferrous oxide or carbonate; it is preferable to rinse the integral organic iron coatings in hot aqueous solutions of an alkaline sulfide, borax, or disodium phosphate to both imbibe fusible flux salts and to form fusible iron salts and fusible sodium salts by ion exchange.

dium sulfite to fifteen parts of oxalic acid with selected for incorporation in the binder.

10 preferably a small amount of manganese dioxide, one fortieth as much manganese dioxide as oxalic acid being a good ratio. The work is dipped in this solution at room temperature or slightly warmer, and the coating should form in a minut or so.

MELTABLE PIcMENrs FOR STEPWISE LUBHICATION According to my present invention, the fixed integral films previously described are coated with a binder through which is distributed various meltable pigments. The pigments must have a Mohs hardness of less than 5 and melt below the melting point of the work or the die, whichever is lower. The pigments generally melt above 500 C. and are various soft and fusible metal compounds.

The pigments in each lubricant are selected in relation to the 'integral film and binder so that there is effective stepwise or graduated lubrication between, the work and die throughout the great portion of the drawing operation. Thus, the binders usually melt below 200 C. to furnish initial lubrication, so that the pigments selected should melt between 200 C. and 1300 C. or roughly, .the melting point of the work if it is low carbon steel. Likewise, the integral film will usually melt around 900C. if a phosphate and around 1050 C. if a sulfide. For this reason pigments melting between 900 C. and 500 C. are

1 The choice of the best combination of integral coating and stepwise lubricant is contingent upon the amount of reduction required in the forming operation. In general, a light reduction of 15 to 25 per cent can be taken upon work coated with a conventional iron phosphate coating of 50 to 150 mg. per sq. ft: or the equivalent light sulfide or-oxalate coating. Fora heavier draft of to 50per cent, a heavy zinc (and iron) phosphate, iron sulfide, or iron oxalate coating of 200 to 1000 mg. per sq. ft.'is to be preferred. With a light coating of iron phosphate or its equivalent that will undergo'a 15 to 25 per cent reduction, a dry lubricant film obtained by immersing the. pre-coated work in a hot aqueous solution of 2 ounces per gallon of sodium tallow soap and 10 ounces per gallon borax, then draining and drying the work, is very satisfactory. To draw the same piece to a greater reduction of, for example, 30 to 40 per cent'it would be preferable to apply the heavier zinc phosphate coating or its equivalent iron sulfide or oxalate layer, and to film the heavier undercoating by immersion in a hot aqueous solution, containing 3 .ounces per gallon sodium tallow soap, 16 ounces per gallon borax, and 2 ounces per gallon precipitated chalk, or an equivalntjusible pigment. The precipitated chalk reacts in the hot borax solution to form a fusible shell of sodium carbonate and calcium borate over each minute particle and is thus equivalent to a fusible pigment.

, If it were necessary to draw this same workpiece to an extreme reduction of to per cent, or to make more than one reduction with-. out recoating the piece, it would likewise be desirable to apply a heavy zinc phosphate or an equivalent heavy undercoating, but aninitial A water insoluble stepwise lubricant would be first applied to the heavy integral undercoating as a. solvent paint or water emulsion consisting of thinner, a thermoplastic binder, and fusilble pig} ments. When this initial water insoluble stepwise lubricant film has dried or set-up, the work is then coated withan aqueous soapj and borax.

type lubricant,v and: drawn to the extreme. reduction. When such duplex lubricant layers. are used. in severe or multiple draftingr the water solublestepwise' lubricant is rolled: back into the: die throat and the. water insoluble thermoplasticbinder and fusible pigments are forced intothe drawn surface to prevent any metal-to-metal contact, and to leave a residual stepwise lubricant film that can be recoated with the water soluble stepwise lubricant, and again drawn. This duplexmethod is shown in Examples XV" and XVI;

As a production cost factor, any appreciable increase indrawing speed or reduction will absorb any-reasonable expenditure for properly coating thework and using the best suited lubricant.

Table I FUSIB'LE, PIGMENTS 12 a fusible natural, synthetic or resinous. material. is preferred.

Corrosive vehicles, 1. e., those containing sulfur; or chlorine, such as solutions or dispersions of chlorinated diphenyl (Arochlor) chlorinated rubber (Tornesit), ethylene polysulfide polymers, chlorinated paraffin, Z-chlorobutadienepolymer (neoprene) and vinyl chloride are especially desirable in that they tend to bond directly tosthe 2 metal through their polar linkages. In addition,

their decomposition under frictional heat willcause the formation of a fusible iron chloride or sulfide as a secondary lubricant.

In lubricating compositions of the present invention, the proportions of pigment and vehicle may be'varied widely to obtain the desired fluidity. Usually, it is preferable to have to 30 parts of vehicle or binder for each 100 parts oil composition, the remainder being pigment and Mobs" Melting 2o solvent. The vehicle is thus considered as the Pigment" SW' residue inrthe fixed film after evaporation of the W v solvent. The pigments generally comprise. from Aluminum stearate.. Al(GiaHi 0z)i-. 1.0 180- two to five tunes amount of vehlcle' Antimony 0xide sbioi j 2.5-3.0 (its Examples of suitable natural and synthetic ig gg gggeg sbzsef-g ggg thermoplastic resins. which may be utilized in Arsenoussulfigleiiii. conjunction with, the suitable fluidity-imparting; Bar um pyropiosp a e. Bismuth Sulfide B G85 agent,.such as a solvent, plasticizer, or dispersm B'oric anhydride. 3:0 517 mixture. are listed below: Calcium tetraborate 3. 0' 986 Calcium stearate' l. 0' lllll Table II Cadmium pyrophos- V 3.5. 900 o i i i t lfid 4 0 1 no o a su Chromium fluoride 4. 5 1, 000 ggg 'i gfi Copper po\vder 225-3. 0 1,003 Melting Copper sulfide. 2.0 l, 130- Range Ferrous sulfide. 3;54.0' Ferrous fluoride 3. Ferrous phosphate 2-3 Lead b0rate 1.5-2.0 I 0. Lead'Chromate 2. 5%. 0 Lead Molybdat 2.

75-115 Lead'oxido (litharge)... PbO 2:5 Alkyl type, 0 3 lfeadiphosppate Alkyl type, modified (rosin, etc.) so- L metaslncatemm" Cellulose acetate (Aceto-butyrate). 60 Lead S111fid( 9.19I12) P 2. 5 1. 120 Cellulose nitrate v 604m. flg g yrop 3- 9 goumamneqndem 75409 a e. I home iiittttittoftitttiii"iififiiiiifi fiiiii Mereury); sulfide (ver.- HgS... e l. (1-1.5 446 Ester gum 70400. mi 1011 Merclurychloride (calo- HgCl l 1. 0-20 302 w g gg gg gghfg g fggs me i Molybdicoxide --1 195 i lt vlfiy ittfitiitiiiififif" 1313..-..-1913. Nickel sulfide NlS 3.0-3.5 797 Polyvinylacetate 10mm. Sulfur S? 0 Chlorinated rubber Molybdenum sulfide. 2.0 1,185 Resins Natural. Vanadium pentox1de V105 2.5 690 Amber 250%) Zinc palmitate 1.0 419 h' h' 90-400 Zinc-borate. 3.0' 980 5G Bifiumen 90410 Zinc phosphate Zni(PO4): H 3.5 900 Gilsonitem" 116i Igatural resins (Dammar, Copal, etc;) 85-150. osiu v About $518118!) 110 axes, natura 40-80 BINDERS Waxes, petroleum Mi 25-60,

Variousv binding materials. are usable in conjunction with the present invention. The binder serves as a vehicle for incorporating the meltable, pigments to distribute them uniformly over the work surface and to protect and lubricate the inner integral film of phosphate or sulfide by acting as an initial lubricant between the work and die over the lower. temperature ranges.

The binding material is preferably a thermoplastic natural or synthetic resin having a melting or softening point below 300 C. The-choice or vehicles and pigments is usually determined by the expenditure that can be made and the severity of service required. When the service not so severe and the expenditure is limited, a heat labile binding material suchas the or-- ganic' colloids which decompose at relatively low temperatures maybe used and the principal reliance for lubrication based upon the fusible pigments. On. the other hand, when there issevere service and suitable expenditures can bemade,

Table III 'THERMOSETTING Rns Ns Melamine or urea-aldehyde-polymers,

Casein-formaldehyde Phenol-formaldehyde Water soluble binders suitable for use with other water soluble or water insoluble pigments are listed? below. These binders are'divided' into two groups'the lubricating or melting binders and the non-lubricating or charting binders which carbonize or decompose at elevated temperatures.

Table IV WATER SOLUBLE LUBRICATING BINDERS Carbowax (a polyalkylene glycol ether) Glycerol and glycol borates and phosphates Glycol stearate Polyalkylene glycol oleate or stearate Sodium palmitate Sodium stearate Sodium oleate WATER SOLUBLE NON-LUBRICATING BINDERS WATER SOLUBLE NON-LUBRICATING BINDERS Sodium naphthenate Starch When a water soluble, non-lubricating binder is usedit is also necessary to use some sort of additional lubricant for the lower temperature ranges (IOU-400 0.).

cutting oils, lubricating oils, soaps of all kinds} Good lubricants for this purpose are the various commercial drawing and.

especially high titre, high tallow soaps, soap and,

borax mixtures, and the thetic waxes.

CONCLUSION From the preceding discussion, it is evident that a wide variety of lubricant compounds andcompositions can be formulated which utilize my various natural and syninvention. In all cases, the formula used should vary with the particular problem presented and the conditions under which it is used. In addition, the relative cost of the compounding materials should be influential in determining exact lubricant components. 7

In order to facilitate complete disclosure of this invention, I am listing a series of examples" of the drawing or deforming of metal. It is understood that the invention is by no means limited thereby and that these are only typical formulas selected from the wide range of com-1' binations of integral coatings and lubricants suc as are above described.

EXAMPLE X THERMALLY FORMED OXALATE A solution of the following composition was made up:

Oz. per gal.

- The'above solution is heated to 115 F. and

a yoke of pickled stainless steel rod immersed inthe solution, and the excess solution allowed* to drain off after a two minute immersion.

There is no noticeable coating action in such a short immersion at such a low temperature,

but a coating of insoluble ferrous and calcium oxalates are formed when the oxalate after drawn through a plurality of successive dies with no further treatment by utilizing a stepwise box soap powder containing a flux and mineralizer and having the following composition:

Sodium stearate 45 per cent 0.15 molar Sodium sulfite 12 per cent 1.10 molar Borax 38 per cent 0.10 molar Moisture 5 per cent This soap is made by crutching ground borax glass and anhydrous sodium sulfite into the sodium stearate after saponification to remove water and then pouring the molten mixture into frames. and grinding the dry soap into a powder.

EXAMPLE XI WATER SOLUBLE SULFIDING LUBRICANT As aforementioned it is possible to forman integral ferrous sulfide coating on articles to be drawn with a reagent that will become also a water soluble stepwise lubricant, when the residual film is dried on thework. Such a combination coating and lubricating bath can be made up by dissolving 8 to 20 oz. per gallon .of the following composition in hot water:

Diethylene glycol stearate or sodium stearate 20 per cent Starch or polyvinyl alcohol 10 percent Boric acid, H BO 0.48 molar 30 per cent Sodium thiosulfate,

Na S O -5H O "0.16 molar 40 per cent The bath is heated up to -200 F. and the degreased carbon steel work immersed in the hot solution for about five minutes, during which time a black iron sulfide film is formed on the surface by the polythionic acid decomposition products. The work is removed, then drained and dried, and the film remaining on the work is a stepwise lubricant by virtue of the polar stearate, protective colloid, and fusible flux salts comprising the dry homogeneous film. The reactions which take place are as follows:

" Polythionate (2) Decomposition on drying: 2NazB O7 4H3B 03 4s 4NaHSO 3N8zB 07 N8zS4 -1 4SO2T (gas) The dried film therefore contains sodium tetraborate and sodium tetrasulfide in addition to the protective colloid and polar stearate lubricant. The coated metal is thereupon deformed by passing it through a die.

EXAMPLE XII WATER SOLUBLE PHOSPHATING LUBRICANT Combination coating reagent and stepwise lubricant similar to that in Example X can be formulated to form an integral phosphate coating on carbon steel, and also deposit a stepwise lubricant film. Such a bath can be prepared by dissolving from 8 to 20 oz. per gallon of the following dry powder. Diethylene g ycol stearate or sodium stearate 20 parts Starch or polyvinyl alcohol 10 parts Mono-sodium phosphate, NaH P0 0.50 molar 60 parts Sodium thiosulfate, Na S O '5H O 0.17 molar 40 parts The bath is heated up to 180 to F. and the degreased articles (steel tubes in this instance) to be phosphated are immersed in the hot solu-' tion for about five minutes, during which-time an integral iron phosphate coating is formed by the mono-sodium phosphate accelerated by so-' dium: bisulfite. acting as a hydrogen depolarizer. Thereactions are.- clarified by these equations:

NagHIE O; 2NaHzPO NaHSOa S Coating acid dep olarizer bricant is thereupon drawn through suitable drawing dies to provide a reduction in size. Several passes are had without intermediate coating and the articles have a bright shiny surface- This combination of. iron phosphate undercoating and water soluble stepwise lubricant is very satisfactory for drawing articles that are to be. electroplated, and which, must be grease free and easily cleaned.

It. should be pointed out that both of the water soluble stepwise lubricants shown in Examples XI and XII' tend to produce alkaline baths under continued use due to the neutralizing action of the iron. being coated, and the breakdown of sodium thiosulfate to precipitated sulfur and Velatile S02 to leave an alkaline NazO residue. Thus, occasional acid corrections must be made to restore coating action, or else the sluggish coating EXAMPLE XV EMULsIoN PAINT LUBRICANT Pounds/ I parts Antimony oxide (M. P. 315 C.) 164 Zinc borate (M.-P. 980 C.) 493 Linseed oil modified Alkyd resin l- 206 Cobalt Linoleate (6% cobalt) 2 Oleic acid a.

Casein 2'1 2-amino methyl propanol 7 Algin 3 Water 392 The above ingredients are mixed in any desired order to provide an aqueous emulsionpaint.

Low carbon steel sheet is first cleaned and then given a phosphatic paint base coating by treatment in a bath of calcium dihydrogen phosphate. The phosphated sheet is then painted with the antimony oxide-zinc borate paint given above. When the painted sheet is thoroughly dry and has formed a fixed solid film it is immersed in bath can be made alkaline by caustic additions I to become a stepwise lubricant similar to Example XIV or XV and a new coating bath made up to replace the acid depleted coating solution.

' EXAMPLE XIII SOLUBLE SOAP AND BORATE PIGMENT EXAMPLE XIV SIILFURIzINe SOAP TYPE LUBRICANT The work is dipped in the stainless steel coating, solution of Example I, left in it for around five to fifteen minutes during which time a black sulfide coating is formed on it. It is then dipped in a 20 per cent water solution of the following dry powder, dried, and deformed by drawing through a die.

. Molarity Percent Soap 0. l Stem 5 NaOH 0.1 4 K2003 0.05 7 Sulfur 0. 3. '9 Nilzszos 0. 1 2O l TazB401 anhydrous 0. l 20 C80 03'; 0. 00 5 a solution of hot paraffin containing 30 per cent calcium stearate. This completely Waterproofs the sheet and leaves a lubricating wax protective layer on the paint. The sheetis then deep drawn into a cylinder on a hydraulic press using a fiowed water coolant and lubricant containing 2 oz. per gallon of sodium stearate: and 2 oz. per gallon of borax. The drawn. cylinder has a highly lustrous finish, free from galling' or scratch marks so that a desirable finish may be applied by mere"- ly a dip or spray with a thin clear'lacquer; The stepwise. lubrication can be: shown to consist of the following progressive melting cooling sequence:

(1) Paraffin melting at C. (2) Calcium stearate melting at C. (3) Water acting as coolant. (4) Alkyd resin vehicle melting at C. (5) Antimony oxide melting at 656- C. (6) Zinc borate melting at 980 C. 7) The phosphate coating melting. around EXAMPLE XVI ETHYL CELLULOSE LUBRICANT PAINT Parts Ethyl cellulose 16 Hydrogenated rosin '8 Castor oil '4 Toluene 54 Hy-fiash naphtha 10 Butanol 8 Ferrous sulfide pigment (M. P. 1193" C.) 24 Nickel sulfide pigment (M. P. 797 C.) 24

reducing atmosphere and. then coated. with theabove pigmented composition. The metal is then. deep. drawn. into acylinder on ahydraulic press using as a. fluid. flowed over the coated. black an aqueous solution of coolant and lubricant. of four ounces of diglycol. stearate per gallon of water.

The article produced has a black, shiny protective surface which can be coated with paints as desired without cleaning.

EXAMPLE XVII CHLORINATED RUBBER LUBRICANT A chlorinated rubber, thermosplastic paint is made up having the following composition;

Parts Chlorinated rubber 20 Chlorinated diphenyl 8 Turpentine 35 Hy-flash naphtha 35 Butanol Cuprous chloride pigment 40 This paint is used to coat a stainless steel rod previously sulfurized as by Example II. Cuprous chloride is used to pigment this formula since it is not adversely affected by any hydrogen chloride which might be evolved by the thermal decomposition of the chlorinated rubber. The rod is drawn to 25 per cent reduction and still has a bright finish after drawing.

EXAMPLE XVIII EMULSION PAINT This is to be considered as only illustrative of the emulsions that can be used.

EXAMPLE XIX BUMPER BAR FORMING LUBRICANT Cold forming has replaced the former hot for ing of automotive bumpers, so that the bumper bar stock can be machine polished in the fiat, and the polished stock phosphated and coated with a water soluble stepwise lubricant that can be readily cleaned off 50 that no defective nickel plating will be caused by any lubricant residues. Since the deformation in this operation is great, it is preferable to use a medium phosphate coating, but since production time is of the essence, it is best applied by an accelerated zinc phosphate bath such as that in Example VIII.

After the bumper stock is phosphated and rinsed, a stepwise lubricant is applied by roller coating, and. the applied lubricant film quickly dried by hot air blast or an infra red drier. A satisfactory composition is the following:

SOLUBLE BUMPER LUBRICANT The above dry powder is made up into a warm soft water solution at a concentration of about 14 oz. per gallon and the solution maintained between 160 and 175 F. for roller or drip application. This type of lubricant is disclosed in the Orozco and Henricks Patent No. 2,469,473.

EXAMPLE XX SOAP AND BORAX LUBRICANT Carbon steel blanks for deep drawing were cleaned in an alkaline cleaner, rinsed, and dipped in cold 15 per cent muriatic acid to a give a minute etch, again rinsed, and then coated in the copper immersion accelerated mono-sodium phosphate coating bath disclosed in Example VII.

After phosphating and rinsing, the blanks were coated by immersion in a boiling solution of 15 per cent sodium tallow soap and per cent borax at a concentration of 1 pound per gallon, and allowed to drain and air dry.

The blanks thus coated were deep drawn into cylinders with excellent die life and very few rejects due to surface imperfections attributed to the drawing operation.

This type of lubrication is disclosed in the Whitbeck Patent No. 2,470,062.

EXAMPLE XXI ALKALINE RINSE Deep drawing stock was phosphated with a light iron phosphate coating in the ammonium dihydrogen phosphate bath in Example VI, which bath also contains calcium salts as well as some iron salts held in solution by the chloride ion as the iron nitrosyl complex. In order to augment the thin iron phosphate coating and to gain additional film pigments, the coated work was not water rinsed in the usual manner. Instead, the coated work still filmed with the coatin solution is dipped in a hot still solution of 4 to 6 oz. 1 gal. of disodium phosphate, and held in the solution for three minutes so that all of the calcium and iron absorbed in the unrinsed coating will be precipitated as insoluble phosphate. The sodium phosphate treated work was then coated in the following sulfurizing soap lubricant, still without rinsing.

Weight Per cent Sodium tallow soap 0. Starcln..-

NazSzOg-5Hz0 Trisodium phosphate Chlorinated pheno1 Carbowax 6000. Pine oil H N) HeeHocwmQmeno The work thus given the alkaline phosphate EXAIVIPLE ICXII SULFURIZING IRON HYDROXIDE COATINGS Wire rod can be sull coated by allowing freshly pickled carbon steel to rust in the air while wet with water or a weak salt brine. Stainless steel can be provided with a hydrated oxide layer by dipping clean pickled stock'in a fused sodium hydroxide bath containing about 10 per cent sodium nitrate and maintained at 900 to 1000" F.

In either case, the hydrated iron oxide is con- .verted to fusible iron sulfide mixture by im- 19 mersion in a boiling polysulfide solution made up from 1 to 3 pounds per gallon of the following calcium sulfide coating:

- Weight Molarity Per cent Calcium hydroxide Ca(OH)q 0. 32 25 Calcium chloride, 0210124120.... 0.16 20 Sulfur flour 1.25 40 Starch to 40 Aryl-alkyl sulionate wetting agent 5 EXAMPLE XXIII SULFURIZED OXIDE COATING FOR WIRE Carbon steel wire is sull coated in the same manner as the previous example or stainless steel wire is given an oxide coating in a fused caustic bath, and rinsed off and dipped in a hot sulfurizing soap lubricant solution such as that disclosed in Example XIII. The coated wire is darkened by immersion in the hot solution, but the hydroxide undercoating is not completely blackened until the soap film is dried in a flash baker after being drained and air dried.

The integral sulfide coating and water soluble stepwise lubricant film formed in this manner is drawn through a stepwise box soap lubricant of the following composition:

Molarity gf gf Calcium stearate. 0.1 40 Calcium hydroxide. 0. 05 36 Iron sulfide FeS 0.05 24 The wire so treated and drawn has a bright gray finish free of any scratches or drawn in lime particles.

While in the aforementioned examples I have usually shown one fixed film over the integral coating of iron salt on the metal, I may use more than one film to obtain further benefits from step-wise lubrication. Thus, the surface of the steel to be worked may be treated with a solution such for example as the baths of Example I containing polythionate materials equivalent to Wackenroders solution to form an integral adhered coating to obtain iron sulfide upon the material. The thus treated metal after rinsing may be then filmed by contacting it with an alkaline earth polysulfide solution containing a colloidal carbohydrate such at starch or polyvinyl alcohol and the like. After drying the latter film on the metal it may be then quickly immersed in an aqueous soap and borax film such as previously described to provide a second film over the previous polysulfide film. The

material thus treated may then be dried and 20 visions of the patent statutes, numerous modi-j fications of the construction shown may be IQ? sorted to without departing from the spirit of this invention.

What I claim is:

1. In the lubrication of a ferrous metal surface which is subjected to sliding friction, the steps which comprise forming on the surface an integral coating by subjecting the surface to sulfur in the presence of a reducing atmosphere, and thereafter disposing over said coating an adherent meltable film deposited from solution and containing a meltable organic binder that is solid at room temperature, and a finely divided inorganic solid compound insoluble in solutions of said binder and having a melting point below the melting point ofiron and of the integral surface coating and a scratch hardness less than 5 on a Mohs scale, whereby said integral coating is protected and also stepwise lubrication is effected when sliding friction occurs and finally working said metal surface and subjecting it to sliding friction.

2. In a process of working ferrous metal the steps which comprise forming on the surface of the metal an integral coating of hexagonal black ferrous sulfide and superimposing on the thus coated metal a fluid composition capable of drying to a solid meltable film and comprising at least one meltable and fusible solid inorganic compound distributed through a fluid vehicle containing an organic binding material, said inorganic compound being insoluble in said vehicle, being meltable at a temperature less than the melting point of the ferrous sulfide and having a Mohs hardness not exceeding 5, drying said fluid composition to a solid film and finally deforming said metal.

3. In a process of deforming a ferrous metal surface, the steps which comprise forming on said surface an integral coating of a solid ferrous compound having a melting point less than that of the ferrous metal and greater than the temperatures at which hydrocarbon lubricating oils are stable and which has a scratch hardness of less than 5 on the Mohs hardness scale, thereafter forming over said surface an adherent coating comprising an organic binder in a solid state but having a melting point lower than that of said ferrous compound of said integral coating and a plurality of finely divided inorganic solids, at least one of which is an inorganic compound, which solids have a lower melting point than the melting point of said integral coating, said organic binder also having a melting point lower than that of said integral coating and that of said finely divided solids, and thereafter subjecting the metal to deformation, whereby said organic binder both protects said integral coating and cooperates therewith and with said finely divided solids to provide stepwise lubrication at different temperatures caused by said distributed therethrough a solid inorganic compound meltable at a temperature below the melting point of the ferrous metal phosphate of said coating and having a hardness not exceeding 5 on the Mohs hardness scale, and thereafter deforming the metal.

5. A method of treating ferrous metal prior to deformation thereof by drawing, which comprises subjecting said metal to contact with an aqueous solution comprising sulfur containing materials formed from sodium tetrathionate in the presence of boric acid to form an integral adherent coating comprising ferrous sulfide on the metal, drying over said integral coating an aqueous liquid comprising an organic water soluble film forming protective colloid and a meltable inorganic compound to form a film that is solid at room temperature, which is deposited from solution and which contains a meltable solid organic binder and a solid meltable inorganic compound having a scratch hardness of less than on the Mohs scale and a melting point less than the melting point of said integral coating and higher than the melting point of said organic binder and thereafter deforming the metal.

6. In the lubrication of metals, the method of forming a lubricant coating on ferrous metal surfaces by the steps which comprise subjecting the metal to contact with an aqueous acidic coating and etching bath containing polythionates to form an integral adherent coating containing iron sulfide upon the metal, the iron sulfide being derived from reaction of the bath upon the ferrous surface, then rinsing the coated metal and then filming the coated metal with an alkaline earth polysulfide solution containing a colloidal carbohydrate, drying the polysulfide and coloid film and then applying an aqueous soap and borax lubricant film over the previous polysulfide film and then drying the lubricant onto the coated metal surface.

7. In a process of working ferrous metal, the steps which comprise (1) forming on the metal surface an integral iron salt that has a lower melting point than the metal, (2) thereafter forming a meltable fixed film over said integral iron salt by coating the surface thereof with a film-forming, liquid composition containing a water-soluble organic binder that dries to a solid film and a meltable, solid inorganic compound, said inorganic compound and organic binder having melting points below that of the integral iron salt and having hardness less than 5 on the Mohs hardness scale and (3) thereafter working the metal, whereby said solid film both protects said iron salt and cooperates therewith to provide, by difference in melting point, stepwise lubrication at the varying temperatures produced by the drawing operation.

8. In a process of working ferrous metal, the steps which comprise (1) forming on the metal surface an integral iron salt that has a lower melting point than the metal, (2) thereafter forming a meltable fixed film over said integral iron salt by coating the surface thereof with a film-forming liquid composition containing a water-soluble organic binder that is solid at room temperature and a plurality of solid meltable inorganic compounds distributed therethrough,

said inorganic compounds and meltable binder having melting points below that of the integral iron salt and a scratch hardness less than 5 on the Mohs hardness scale and (3) thereafter working the metal.

9. In a process of working ferrous metal, the steps which comprise 1) forming on the metal surface an integral iron salt that has a lower melting point than the metal and a hardness less than 5 on Mohs hardness scale (2) coating the surface thereof with a film-forming aqueous solution containing a water-soluble organic binder and a plurality of water-soluble, inorganic compounds which remain distributed through the binder upon drying, said binder and inorganic compounds having melting points below the melting point of the integral iron salt and a scratch hardness less than 5 on Mohs hardness scale (3) drying said solution to form a solid-at-room-temperature, meltable, fixed film over said integral iron salt and (4) thereafter working the metal.

10. A method of treating ferrous metal which comprises subjecting said metal to contact with an acidic aqueous solution containing (1) colloidal sulfur, sulfur dioxide, and a mixture of polythionic acids, (2) a water-soluble protective colloid, (3) a water-soluble,lubricating organic binder, and (4) a member of the group consisting of fusible borates and phosphates, so that an integral coating is formed on the metal while in solution, then with-drawing the metal from said solution so as to leave an overlying film of organic binder with fusible borates and phosphates therein drying said film on the ferrous metal, and thereafter deforming said metal with the aid of a die.

11. The method of claim 7 in which the integral coating comprises an iron sulfide.

12. The method of claim 7 in which the integral coating comprises an iron phosphate.

13. The method of claim 9, inwhich the integral iron salt is water insoluble.

JOHN A. HENRICKS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,067,530 Ihrig Jan. 12, 1937 2,223,037 Ihrig Nov. 26, 1940 2,350,491 Butler et a1 June 6, 1944 2,469,473 Orozoco et a1 May 10, 1949 FOREIGN PATENTS Number Country Date 367,198 Great Britain Feb. 18, 1932 496,866 Great Britain Dec. 7, 1938 279,534 Germany Oct. 21, 1914 

8. IN A PROCESS OF WORKING FERROUS METAL, THE STEPS WHICH COMPRISE (1) FORMING ON THE METAL SURFACE AN INTEGRAL IRON SALT THAT HAS A LOWER MELTING POINT THAN THE METAL, (2) THEREAFTER FORMING A MELTABLE FIXED FILM OVER SAID INTEGRAL IRON SALT BY COATING THE SURFACE THEREOF WITH A FILM-FORMING LIQUID COMPOSITION CONTAINING A WATER-INSOLUBLE ORGANIC BINDER THAT IS SOLID AT ROOM TEMPERATURE AND A PLURALITY OF SOLID MELTABLE INORGANIC COMPOUNDS DISTRIBUTED THERETHROUGH, SAID INORGANIC COMPOUNDS AND MELTABLE BINDER HAVING MELTING POINTS BELOW THAT OF THE INTEGRAL IRON SALT, AND A SCRATCH HARDNESS LESS THAN 5 ON THE MOHS'' HARDNESS SCALE AND (3) THEREAFTER WORKING THE METAL. 